WORKING LIFE OF LIGHTBULT IS DISTRIBUTED WITH MEAN OF 13 YEA

WORKING LIFE OF LIGHTBULT IS DISTRIBUTED WITH MEAN OF 1.3 YEARS AND STANDARD DEVIATION OF 0.3 YEARS. WHAT IS PROBABILITY THAT IT WILL LAST AT LEAST 1 YEAR?

Solution

We first get the z score for the critical value. As z = (x - u) / s, then as          
          
x = critical value =    1      
u = mean =    1.3      
          
s = standard deviation =    0.3      
          
Thus,          
          
z = (x - u) / s =    -1      
          
Thus, using a table/technology, the right tailed area of this is          
          
P(z >   -1   ) =    0.841344746 [ANSWER]